1. Field of the Invention
The invention relates to the distribution of a wireless signal through an enclosure.
2. Description of Related Art
Cellular wireless is an increasingly popular means of personal communication in the modern world. People are using cellular wireless networks for the exchange of voice and data over cellular telephones, Personal Digital Assistants (PDAs), cellular telephone modems, and other devices. In principle, a user can seek information over the Internet or call anyone over a Public Switched Telephone Network (“PSTN”) from any place inside the coverage area of the cellular wireless network.
In a typical cellular wireless network, an area is divided geographically into a number of cells and, in turn, sectors. Each cell contains one or more base stations, which communicate with the mobile stations (such as a cellular telephone, pager, or appropriately equipped computer) within the cell. The base stations in the cells are in turn coupled to a base station controller (BSC), which is then coupled to a telecommunications switch or gateway, such as a mobile switching center (MSC) for instance. The MSC may then be coupled to a telecommunications network such as the PSTN (public switched telephone network) or the Internet.
A base station contains an antenna assembly, amplifier, transceiver and other equipment used to communicate with the mobile stations and the MSC. Each cell is defined by a radio frequency (RF) radiation pattern from its respective base transceiver station (BTS, or “base station”) antenna. Typically this RF pattern is different than the pattern used by adjacent cells. When a mobile station is positioned in a cell, the mobile station communicates via the RF air interface with the BTS antenna of the cell. This air interface communication can occur over control and traffic channels as defined by an accepted protocol.
Many wireless telephone users are familiar with the problems associated with trying to use wireless telephones inside buildings, tunnels, or other enclosures. These enclosures substantially attenuate the wireless signals transmitted by the base stations located outside. As a consequence of the attenuation, inside such enclosures service often becomes less reliable, with calls being dropped or signal quality being degraded. Service may even become completely unavailable, with the result that the user is unable to send or receive any calls.
One approach used to overcome these difficulties is to increase the power transmitted by the base station. A disadvantage with this approach, however, is that the increased power can lead to increased interference in adjacent cells. This, in turn, can decrease the capacity of the wireless network. The power increase can also interfere with other wireless devices in use around the base station. The magnitude of the power increase proportionally affects the amount of interference produced by the base station, with a greater power increase causing a greater interference.
Also, this approach would only solve half of the problem. Increasing the signal strength from the base station would allow a mobile unit to receive the base station's signal in areas that highly attenuate that signal. It would not aid the base station in receiving a signal from a mobile station. Cellular service is primarily a bi-directional mode of communication. To establish a connection in common devices like cell phones, the base station sends control signals to the mobile unit, which responds by sending additional information back to the base station. Using the defined two-way communication protocol, a connection is established. Therefore, in order to support bi-directional communication, an increase in the transmission power of the base station would require a corresponding increase in the transmission power of the mobile station.
Another approach is to provide a distributed antenna system in the enclosure. In this approach, a hub is connected, via wired links, to one or more wireless access points in the enclosure. The wired link is typically a coaxial cable, a 10Base-T cable, or a fiber optic cable.
The hub transmits the RF signals from the base station to the wireless access points, via the wired links. The wireless access points, in turn, transmit the RF signals into the enclosure, where they may be received by wireless telephones. Similarly, the wireless access points receive RF transmitted by the wireless telephones and transmit the RF to the hub, via the wired links. The hub, in turn, transmits the RF to the base station. In this way, the wireless coverage area provided by the base station may be extended into the enclosure.
A disadvantage with this approach is that cabling is often difficult and expensive to install. This is especially true in buildings and underground areas where cabling may have to be installed inside walls or in other difficult to access areas.
Another disadvantage with this approach is its inflexibility resulting from the use of dedicated wired connections. A wired network is not easy to reconfigure, as additional cabling must be installed.